Overview

LIFDI is one of the softest ionization techniques for Mass Spectometry. It can exhibit the true molecular mass in cases where other ionization techniques fail.

LIFDI provides information on liquids and mixtures even in cases where X-Ray is inapplicable and/or NMR and elemental analysis give ambiguous results.

LIFDI is much faster than X-Ray. The analysis can be performed in minutes. Time-consuming sample preparation is not necessary.

LIFDI gives clean spectra exhibiting the intact molecular ion as base peak. There is no matrix interference or chemical background that complicate the interpretation of spectra.

LIFDI can benefit from collision-induced dissociation (CID) to provide further structural information.

LIFDI ionizes polar and non-polar, volatile and non-volatile, reactive and inert samples in solid, liquid or gazeous state of aggregation.

Ionization method

LIFDI is an ionization technique removing an electron from the analyte molecule due to a very high electric field strength like FI/FD.

This image shows a LIFDI probe tip with extraction electrode, emitter and LIFDI-capillary.

The sample is supplied through the capillary and deposited onto the emitter wire without breaking vakuum. A voltage of 10kV is applied between the wire and the extraction electrode.

The LIFDI emitter is composed of a thin tungsten wire onto which thousands of micro graphite dendrites are grown. The tips of the graphite dendrites have diameters in the nanometer range.

The field strength at the tips of the dendrites is four orders of magnitude higher than it would be on a flat electrode at the same voltage. Thus the ionization efficiency is considerably increased: The electrical field is high enough to remove the weakest bound electron from the molecule. Excess energy is therefore not transfered to the ion. Thus cold, not excited M+• ions are generated.

The soft ionized, not excited radical ions can be very reactive. Even low energy collisions with gas particles can therefore lead to fragmentation. Low ion energy and appropriate low pressure of thermalization gas determine the degree of collision induced fragmentation. This can be used for additional structural information.

Applications

LIFDI ionizes polar and non-polar, volatile and non-volatile, reactive and inert samples in any state of aggregation. Even if LIFDI is applicable to a broad range of applications, it is basically used for difficult samples that other ionization techniques are unable to analyze. Those can be found in classes of: